1. Field of the Invention
The present invention pertains for a method and apparatus for performing continuous tubing operations. More particularly, the present invention relates to a system for performing continuous tubing operations in connection with subsea wells and pipelines. More particularly still, the present invention pertains to a continuous tubing system that can be used to pump fluid(s) into subsea wells or pipelines, or that can accommodate fluid flow from said subsea wells or pipelines.
2. Brief Description of the Prior Art
Continuous tubing systems—commonly referred to as “coiled tubing units”—are well known by those having skill in the art of oil and gas operations. Such coiled tubing units, which often provide a viable alternative to conventional rig operations, typically employ a continuous length of flexible tubing rather than multiple sections of rigid pipe.
Coiled tubing can be used to conduct many different downhole operations in oil and gas wells. For example, coiled tubing can be concentrically inserted into an existing wellbore in order to clean out sand or other debris from such well. Further, conventional coiled tubing can be used to conduct downhole operations by attaching a fluid activated tool to the distal end of the tubing, and then pumping pressurized drilling fluid through the coiled tubing to actuate such tool. In the case of a mud motor and drill bit, the drill bit and hydraulic mud motor are lowered into the borehole as the coiled tubing is spooled off a reel, thereby allowing the borehole to be drilled deeper into subterranean formations.
A significant advantage of coiled tubing operations over conventional rig operations is that the coiled tubing can be raised and lowered in a borehole at rates up to ten times faster than those possible with conventional rig techniques. This increased speed is primarily attributable to the fact that coiled tubing can be “tripped” in and out of a borehole without screwing or unscrewing individual joints of pipe during the pipe running process. Put another way, continuous coiled tubing can be translated in and out of a wellbore without having to stop to add or remove individual joints of pipe.
During conventional coiled tubing operations, a continuous length of spooled tubing is typically translated into and out of a wellbore. In most cases, such flexible tubing is stored on a large reel that rotates about a substantially horizontal axis. The coiled tubing can be translated in and out of a wellbore in a virtually continuous manner using a pushing/pulling device known as an injector head.
Conventional injector heads typically utilize specially-adapted chain assemblies to grip the outer surface of the coiled tubing string. A hydraulic drive system provides power for running and retrieving the continuous tubing string into and out of a wellbore. In most cases, the base of the injector head is secured to wellhead pressure-control equipment, while a gooseneck assembly mounted on top of the injector head is often used to feed the tubing string from the reel around a controlled radius and into the injector head.
In most instances, the continuous tubing on the reel is connected to a swivel pump-in sub at one end, while the other end of said continuous tubing can be translated from said reel through the injector head and into a wellbore. Fluids can be pumped through said swivel pump-in sub and into the control bore of the continuous tubing string. During operation, the distal end of the continuous tubing can be translated into said wellbore using the injector head.
As the world's supply of easily accessible oil and gas reserves becomes depleted, significant oil and gas exploration and production operations have shifted to more challenging environments, including deep-water locations. Wells drilled on such locations are often situated in thousands of feet of water, which makes setting of conventional production platforms extremely difficult, if not impossible. In such cases, wells are frequently completed using “subsea” completions wherein the wellheads and related equipment are situated on the sea floor. An extensive array of flow lines are typically used to connect such subsea wells to floating production facilities, pipeline interconnection points and/or other subsea completions.
When servicing subsea wells and/or pipelines, it is often beneficial to insert a hose or other tubing concentrically within the wellbore and/or pipeline, especially to permit a flow path for fluid in said well or pipeline. If the water depth is such that use of a standard hose assembly is not feasible, coiled tubing units are sometimes used. However, conventional coiled tubing units in general, and injector heads in particular, are typically not well suited or cost effective for such uses. Thus, there is a need for an apparatus that can be used to deploy multiple strings of continuous tubing in a well or pipeline, including but not necessarily over the side of a marine vessel or through the moon pool of a vessel, without the need of a separate lifting or translating device such as an injector head.